Leaving aside the probability of a very major shock then the next resident of the White House will be one of the seven contenders featured above. And for each next Thursday night could be crucial. For one or two victory in their party’s caucuses is absolutely central if they are to stay in the race. For others a convincing performance could be a knock-out blow to other challengers.

But how can you call such a complex voting system where not only do you have to get your supporters out but they need to be involved in a public act, in many cases amongst friends and neighbours, in order to make a difference?

As we saw in 2004 with Howard Dean a candidate can go into the Iowa caucuses with big poll leads and come out in third place. It was that night that propelled John Kerry into a position where he quickly became unassailable. The contender in second place then, John Edwards, has clearly learned the lesson and has devoted himself almost totally for several years to his Iowa campaign.

What about Obama? Could Thursday night be the moment when he demonstrates that the colour of his skin will not be a handicap to electoral success? Again he has put everything in and the stakes are very high. If he does not win then his aim, surely, is to ensure that he is the only viable anti-Hillary candidate.

At the moment the latest polls have all three pretty close but with Hillary having a small lead. There’s one bit of good news for Obama and that is that some surveys have shown him ahead amongst those who have been to a caucus before. The bad news for him is that a lot of his support comes from the young who are the least likely to go through the bother of actually attending.

The GOP race is equally fascinating. Huckabee’s polling leads are being squeezed but he does have considerable support amongst the state’s evangelical Christian communities and my guess is that they are probably going to be more likely to caucus. For Romney a good performance is absolutely crucial.